The present invention relates to an improved process for manufacturing cellular plaster obtained by calcining phosphogypsum.
Phosphogypsum is a by-product of the commercial production of phosphoric acid by reacting sulfuric acid with phosphate rocks.
It is already known to prepare cellular plaster by mixing plaster with a foam obtained by stirring water with a surfactant. Cellular plaster has already been prepared by mechanically mixing plaster, water and the foaming agent, the foam being prepared in situ. It is also known to prepare the foam separately by stirring the surfactant with part of the water necessary for wetting the plaster, the foam being added to the partly wetted plaster.
The foam is preferably mixed with dry plaster, the whole quantity of water necessary for wetting plaster being introduced as foam. The latter process has the advantage of providing a cellular plaster having improved mechanical characteristics.
It is also already known to add to the plaster mixture, at any step of the manufacture process, additives such as colloids, fungicides, waterproofing agents and/or retardants.